A Queen Elizabeth build sounds like an idea.
Does it have to be narrowed down? Can't you do anything that, however loosely, has a connection?
OK, how about this?
'In the Service of Her Majesty' - Any vehicle, What-If or Real World, as in aircraft, ship, fighting vehicle and transport, space vehicle, both military or civilian, that would have served in any of the armed forces of nations of which the Queen was Head of State, or used by Her Majesty to travel anywhere in the world, during the period of her reign.
Examples might the dirigible the young Queen used during her first tour of the Empire, or the shuttle she rode in for her visit to the British Lunar colony, or one of the Queen's Flight's Concordes.
Military subjects might be RCAF Avro Arrows, 'Red Arrows' CAC trainer jets, British Army JagdChieftain tanks, or the original CVA-01 HMS Queen Elizabeth.
Airfix have of course recently released the 'Katy' ambulance she learnt to drive in.
I'm happy to Mod this one, after all, it was my post that sort of started it all, just be aware that it's my first GB Mod on this Forum, so I may need back up . . .
cheers,
Robin.